Modeling is an essential discipline, especially in software engineering. Students and developers alike employ models to describe systems, capture requirements, and communicate with other teams. For that purpose, UML diagrams are often employed. Meanwhile, mobile devices increased in prevalence and popularity and flexible work arrangements were introduced in a larger number of workplaces. Effective collaboration is more important than ever. However, tools have not kept up with these developments. To the best of our knowledge, there is no semantics-aware mobile modeling approach that supports collaboration in real time: a gap we aim to close in this paper. For this, we investigate existing approaches for mobile modeling and their shortcomings with a particular focus on conflict-free, real-time collaboration. Based on our findings, we conceptualize and implement CoMod, a proof of concept allowing users to collaboratively edit UML class diagrams in real time. The system consists of a Flutter-based client application for Android and iOS and a Node.js-based server executable. These components utilize conflict-free replicated data types (CRDT) to merge participants’ changes.